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Thermal diffusivity of orthopyroxenes and protoenstatite as a function of temperature and chemical composition

Anne M. Hofmeister
Thermal diffusivity of orthopyroxenes and protoenstatite as a function of temperature and chemical composition
European Journal of Mineralogy (August 2012) 24 (4): 669-681

Abstract

The phonon component of thermal diffusivity (D) was measured up to temperatures (T) of approximately 1000-1500 K from laser-flash analysis from four chemically distinct, gem quality single crystals and six cleavage flakes or mats of orthopyroxenes, plus synthetic protoenstatite. From electron microprobe analysis, Mg/(Mg+Fe) varies from 0.65 to 1.0 and Al, Mn, Cr, Ti, and Na occur as minor impurities. From visible spectroscopy, Fe (super 3+) content is small to negligible. From near-IR spectroscopy, hydroxyl contents range from approximately 0 to 600 ppm. Heating large crystals redistributes H (super +) among various sites: thus, thermal history influences speciation. For Mg/(Mg+Fe) approximately 0.9, at 298 K, D is 1.8, 1.9, and 3.2 mm (super 2) s (super -1) along [010], [100], and [001]. For all samples, D decreases with increasing T. Roughly, anisotropy is independent of T, and unaffected by transition to the protoenstatite structure, which causes D to drop by approximately 10%. Low-order polynomials describe D (super -1) (T) for orthopyroxenes. A second-order polynomial describes the dependence of D (sub 298) on Mg content. Only 300 ppm OH suffices to lowers D by approximately 10% whereas Fe (super 3+) makes D decrease more rapidly with T but coupled Al substitution has the opposite effect. Available heat capacity and volumetric data were used to calculate orthopyroxene and protoenstatite thermal conductivity.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 24
Serial Issue: 4
Title: Thermal diffusivity of orthopyroxenes and protoenstatite as a function of temperature and chemical composition
Author(s): Hofmeister, Anne M.
Affiliation: Washington University, Department of Earth and Planetary Sciences, St. Louis, MO, United States
Pages: 669-681
Published: 201208
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 38
Accession Number: 2012-073266
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201238
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